The newly identified capacity for wind to spread it opens up a potential route by which the viruses can spread between farms.

The finding came about after Dutch researchers studied an outbreak of the avian flu strain H7N7 in poultry on Dutch farms in 2003, which resulted in 89 confirmed human infections including one death.

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Computer models showed that wind patterns at the time of the outbreak explain how different genetic variants of H7N7 ended up on different farms (Journal of Infectious Diseases, doi.org/j3b).

H5N1 is the most harmful strain of avian flu, having killed 360 of 610 infected people since it was discovered in 2003. The fact that a related strain can travel on the wind suggests that H5N1 can too, says Marion Koopmans of the Dutch National Institute for Public Health and the Environment in Bilthoven, who coordinated the research project. “You must assume that this same potential is there for H5N1,” she says.